1. Field of the Invention:
The present invention relates to a video signal processing device for converting an analog video signal from a video signal source into a digital video signal based on preset input and output conditions.
2. Prior Art:
Computerized medical diagnostic imaging systems such as CT scanners are capable of forming images of internal local regions of human bodies. The image information produced by such imaging systems is highly convenient for doctors because it can provide a clear view of the internal structure of the human body. A CT scanner employs a CRT or the like for displaying obtained image information, based on which the doctor makes a medical diagnosis of the examined human body. The image information displayed on the CRT may be thermally recorded on a heat-sensitive medium, thereby producing a hard copy which may be available for medical diagnosis at any time and in any place. An image signal, which represents image information and is supplied from an image signal source such as a CT scanner, is usually applied as an analog video signal to an image output device such as a thermal printer or the like. The image output device converts the applied analog video signal into recording data to be thermally printed, and then records the data on a heat-sensitive medium through a thermal head.
There are known various known computerized medical diagnostic imaging systems which supply analog video signals to image output devices. They include, in addition to a CT scanner, a nuclear magnetic resonance imaging system and other imaging systems. Analog video signals produced by these different types of computerized medical diagnostic imaging systems may have different number of scanning lines, or may have different aspect ratios for reproduced images, even if they have the same number of scanning lines.
When a reproduced image is to be produced, it may be desirable to record image information represented by a plurality of frames on a single recording medium. Such a multiple image format is advantageous especially when image information in a plurality of frames in the vicinity of a certain body region to be diagnosed is observed for greater accuracy of diagnosis.
Therefore, images to be produced have different dimensions when analog video signals have different numbers of scanning lines, different aspect ratios, and different number of frames to be reproduced on a signal recording medium.
When a recorded image is to be produced by an image output device, therefore, it is necessary to produce recording data to be thermally recorded, taking into account an input condition represented by the number of scanning lines of an analog video image, and output conditions represented by the number of frames to be recorded on a recording medium and an aspect ratio of the recorded image.
To meet the above requirement, the analog video signal which is applied to an A/D converter of the image output device must be converted into a digital video signal with sampling pulses which have frequency determined depending on the number of scanning lines, the number of frames, and the aspect ratio, as referred to above. If the frequency of sampling pulses is inappropriate, then the reproduced image may be expanded or reduced horizontally in size.
Heretofore, once the type of an analog video image source, the number of frames to be recorded, and an aspect ratio of an image to be recorded are given, the frequency of sampling pulses is determined by the operator through manual adjustments of a rheostat connected to a voltage-controlled oscillator (VCO) while the operator observes the image as it is recorded. According to another conventional practice, the number of sampling pulses contained in one period (1H) of a horizontal synchronizing signal is manually adjusted to determine the frequency of sampling pulses by the operator while observing the image as it is recorded.
According to these known manual processes, however, the setting of the rheostat or the selection of the number of sampling pulses to be contained in one period (1H) of the horizontal synchronizing signal has to be determined on a trial-and-error basis by the operator while viewing the image being recorded. Therefore, the manual determination of the frequency of sampling pulses has been quite troublesome and time-consuming. Such an adjustment operation must be carried out each time the image output device is connected to a different analog video signal source or an image is to be reproduced in a different number of frames. As a consequence, it has been difficult or cumbersome to display or record images while matching various different conditions.